With aging you can expect to lose muscle size and strength, which increases risk for lifestyle diseases and disabilities (GeroScience, 2020;42:1547–1578), such as:
• heart attacks (Eur Geriatric Med, 2016;7(3):220–3)
• diabetes (Med J Aust, 2016;205(7):329–33)
• osteoporosis and fractures (Arch Endocrinol Metab, 2015;59(1):59–65; J Gerontol A Biol Sci Med Sci, 2018;73(9):1199–204)
• depression and memory loss (GeroScience, 2020;42:1547–1578)
• loss of physical independence (J Nutr Health Aging, 2020;24(3):339–45; 2019;23(2):128–37)
Progressive loss of muscle starts at about 25 years of age. It is caused mainly by a loss of muscle fibers and to a lesser extent by a reduction in type 2 strength fast twitch fibers (J of the Neur Sci, April 1, 1988;84(2-3):275-294).
Why You Lose Muscle with Aging
Every muscle in your body is made up of thousands of muscle fibers just as a rope is made up of many strands. Every muscle fiber is innervated by a single nerve. With aging you lose nerves, and when you lose a nerve attached to a muscle fiber, that muscle fiber is lost also. A 20-year-old person may have 800,000 muscle fibers in the vastus lateralis muscle in the front of his upper leg, but by age 60, that muscle would probably have only about 250,000 fibers. For a 60-year-old to have the same strength as a 20-year-old, the average muscle fiber needs to be three times as strong as the 20-year-old’s muscle fibers. You cannot stop the loss of the number of muscle fibers with aging, but you certainly can enlarge each muscle fiber and slow down the loss of strength by exercising muscles against progressive resistance, using strength-training machines or by lifting weights (Experimental Gerontology, August 13, 2013)….